Nearly all reported ultrathin microfabricated membranes are made of silicon nitride (SiN) (Deshmukh et al., “Nanofabrication Using a Stencil Mask,” Appl Phys Lett 75:1631-1633 (1999); and Toh et al., “Fabrication of Free-Standing Nanoscale Alumina Membranes with Controllable Pore Aspect Ratios,” Nano Lett 4:767-770 (2004)). This is because it is well known that the most commonly available anisotropic silicon etchant, potassium hydroxide (KOH), will not attack SiN. Therefore, a very large thickness of silicon (substrate) can be etched away while leaving a very small thickness of SiN, enabling the formation of thin membranes. Although SiN is an excellent material choice for many applications, having no simple alternatives limits process design flexibility.
Therefore, it would be desirable to develop a method for making ultrathin membranes, where the method can be used to fabrication ultrathin membranes formed of various materials.
The present invention is directed to overcoming this and other deficiencies in the art.